Fuel efficiency in trucks is highly dependent on drag. This is because when a truck travels at speeds of over seventy miles an hour, over sixty percent of its fuel is used in overcoming drag. For example, a modern Class 8 tractor-trailer truck can weigh up to 80,000 pounds, and have a drag coefficient of around 0.60 when traveling at the common United States (US) highway speed of seventy miles per hour (mph). At this speed, approximately sixty-five percent of the truck's fuel is expended for overcoming drag.
Various drag reducing mechanisms have been proposed. However, these drag reducing mechanisms exhibit drawbacks in that they are fixed to the vehicle and can not be moved during the time the vehicle is in motion, and are not controlled based on the location of the vehicle.